Women of child-bearing age are extensively employed in a wide variety of occupations. There have been very few studies which provide information on the relationship between hazards in the workplace and pregnancy outcome. The Collaborative Perinatal Project of the National Institute of Neurological Diseases, Communicative Disorders and Stroke was a prospective study of pregnancy outcome which included occupational histories on 39,215 pregnant woman. The project has continued to study the mother and development of the child for 8 years following delivery. From the available data tapes we will identify those in the Collaborative Perinatal Project who reported exposure to occupational hazards. The most appropriate classifications for analysis of variables will be established as they pertain to pregnancy history, placental characteristics and the growth and development of the children who were born, by the use of multiple regression, multivariate, discriminate and cluster analysis. Those occupational conditions which appear to show associations with adverse pregnancy outcome will be examined in more detail. There is no other comparable set of data which provides such detailed information of the relationship between exposure to occupational hazards and the effects on the developing infant. The continuing evaluation of threshold limit values for chemical exposures and standards for physical stress is dependent upon reliable information on the safety of the workplace for the worker and the child in utero.